The present invention relates to improvements in pneumatic tires whose reinforcement comprises at least one oblique folded ply of metal cables and to the metal cables reinforcing the said ply.
French Patent No. 1,427,886 describes a tread reinforcement intended for tires of the type referred to above, which is formed, in principle, of two oblique plies. One of said piles is reinforced with relatively rigid cables, while the other ply, which is folded around the edges of the first ply, is reinforced with relatively flexible cables, possibly metal cables. Such an arrangement facilitates the folding of the folded ply and avoids damage to the cables in the region of folding.
U.S. Pat. No. 3,949,799 relates to a special arrangement of the cables in a tread reinforcement formed of at least one folded oblique ply reinforced with metal cables. This arrangement is intended to remedy fatigue breaks of the cables in the region of the folding. It is assumed, on the one hand, that a ply of S type and a ply of Z type are plies the cables of which have an inclination in the same direction as the central portion of the letter S and of the letter Z, respectively, as seen by an observer located on the outside of the tire, and, on the other hand, that a cable of S type and a cable of Z type, respectively, are cables, the visible part of each strand (or of each wire, in the absence of strands) of which has an inclination in the same direction as the central portion of the letter S and of the letter Z, respectively, then the arrangement disclosed in U.S. Pat. No. 3,949,799 has as its purpose to untwist the cables in the folded region of the said tread ply. For this purpose, it is recommended to arrange the folded portion or portions of this ply on the outside (with respect to the tire) of the nonfolded portion when said ply appears of the same type (S or Z) as the said metal cables but, on the other hand, on the inside (with respect to the tire) of the nonfolded portion when said ply appears of a type (S or Z) different from that (Z or S) of the said metal cables. The research of the applicant has led to the discovery that the use of a cable of a special structure could provide a substantial improvement in the fatigue strength of the cables in the region of the fold of the folded plies not only when these plies are used in tread reinforcements but whatever the region of the tire in which such plies are used.